Dude, April 1st is more than a week away. You're killing here. You da Capitan. YOU are responsible for spotting things like dogs, cars or timed out lights. My Stoker is totally blind so she is completely off the hook on the 'second pair of eyes' score, but even so, there are primary responsibilities and secondary ones, noticing that the address you are looking for and/or navigation in general might be something to delegate to the Co-pilot but, again, traffic signals are YOUR responsibility. The Stoker never comes off the seat except AFTER a full stop. So there is no need to warn them of a full stop. We have one command for stops and it is all purpose. I could mean stop pedaling and we are going to coast for awhile, or it could mean stop pedaling we are going to stop right now. Stopping simply means stop pedaling. Tandeming is supposed to be an enjoyable activity for Captain and Stoker both. I shouldn't tell another Captain how to run his rig but I can suggest, don't overthink it. Me and mine have a LOT of miles twogether albeit compressed into about 12 years because we only met 12 years ago and do not drive so our various tandems function as transportation, sport and also recreation. We are on a tandem of some kind, every single day. I don't think we use more than a half dozen commands. Most of the time we are just chatting about stuff. So ... commands.

We use the 'Proper Method'. It really works. I get my leg over the top tube but do not take the saddle, obviously. If you can take the saddle without being underway it is too low. Once I'm on, I say "I'm on. I have to because she can't see that I am. You're good there. She then gets on and gets her feet into the PowerGrips. This requires rotating the pedals, so I get my feet out of the way so they can turn as needed. Then I secure my right foot in the PowerGrip (or clip in on the racing tandem), push off and we are underway. The first official command that comes up is usually:
FOOT: Means I need to stop pedaling for a moment to clip in me left foot, arrgh. It is about the only redundant command in our retinue. STOPPING could just as easily work.
STOPPING: pedal rotation, for any reason. and there is no 'starting' command. If I resume pedaling after a coast I just do it. It has never been a problem.
GEARS: Front shift, reduce pedal pressure to next to nothing. Rear shifts get no command. No command needed to resume nominal cadence either.
BUMP: Only major bumps are called out. Apologies are made for significant bumps not called out.
POWER: Self explanatory. Gimme all you got, arrgghh. Now!
SIGNAL LEFT (followed by CANCEL just before we actually heel over for the turn so she can get both hands back on the bars through the turn. While she is signaling she periodically says SIGNALING mainly because I might forget to cancel and she hates taking turns one handed.)
SIGNAL RIGHT (as above) The CANCEL command is the only one that needs a response. If it is not responded to with a CANCELLED then it will be repeated until acknowledged.

I might be the rare Captain who had less (zero) tandem experience than my Stoker but, as Captain, it was (is) my job to Captain with confidence and good judgement. My Stokers previous Captains never gave consistent commands. I thought we should have a consistent set. They have evolved over time. Our second date was a 12 mile ride on a rented tandem. With terrible brakes. We had little to no conversation prior to the ride about teamwork or any other thing about tandeming. We just rode. I could ride a bike. A tandem was just a bigger, heavier, less zippy, roadbike. Make your first ride(s) easy, short(ish) and fun and if it is going to get serious you will know. Good luck.